The objectives of the proposed research are to learn more about human ocular motor disorders that impair the vision necessary for everyday activities, and to appraise therapeutic measures. The research strategy is to (1) relate reliable measurements of eye movements to visual complaints of patients; (2) study natural behaviors such as combined eye- head tracking; (3) use measurements of normal and abnormal eye movements to test mathematical models that are based on known physiological properties; (4) apply new knowledge of pathogenesis to the diagnosis and treatment of disorders of ocular motility. This proposal has five aims that emerge from prior work. The first project is to study the effects of convergence upon acquired forms of nystagmus and so determine the potential therapeutic role of spectacle- prisms. The second project is a double-blind trial of transdermal scopolamine as treatment for acquired forms of nystagmus. It has been shown-that intravenous scopolamine suppresses pendular and downbeat- nystagmus, but a trial of this drug administered in a convenient and safe way is needed. The third project is an investigation of the effects of electronic manipulation of the latency of visual feedback on the onset and maintenance of smooth pursuit eye movements in normal subjects. The same technique will be used to study the oscillations of acquired pendular nystagmus, which have been attributed to abnormal delays in the visual system. The fourth project concerns tests of models for combined eye-head tracking, using stimuli that combine such tracking with high- frequency head vibrations. During everyday activities, subjects often track a moving object with eyes and heads while they are in motion. Normal subjects and patients with impaired vestibular or ocular pursuit function will be studied. The fifth project is an investigation of torsional gaze holding (neural integrator function) during head rotations in roll (the frontal plane). Torsional eye movements have unique properties that can be related to the visual demands that they serve. Dynamic and static ocular counterrolling will be measured in normal subjects and in patients with brain stem disease. Thus, these projects will provide: (1) new information on the pathogenesis and treatment of acquired forms of nystagmus, and the influence of novel visual stimuli on these oscillations; (2) new insights into how combined, eye-head tracking allows vision of a moving object while subjects (and patients with visuo-vestibular disease) are in motion; (3) quantification of gaze control during head rotations in roll, in normal subjects and patients with disturbances of torsional eye movements.